Athletes looking for a performance boost appear to be turning to a little blue pill more usually taken for its off-the-field benefits: Viagra.

But experts are divided over whether it actually offers athletes an edge.

Some sports authorities say the drug is now finding a following among athletes. It isn't clear how many might be taking it in hopes of improving athletic performance.

It also has attracted the attention of the World Anti-Doping Agency. The agency is studying Viagra's effects in athletes, but hasn't yet banned it. Viagra is not on the International Olympic Committee's list of prohibited drugs, so athletes can take it at the Beijing Olympics.

Viagra, also known as sildenafil, is manufactured by Pfizer Inc. It originally was developed as a heart drug; its use as a treatment for erectile dysfunction was accidentally discovered.

The drug works by increasing the effects of nitric oxide, which makes blood vessels expand. That should theoretically allow blood cells to get more oxygen from the lungs. It also might improve heart function.

But whether Viagra makes athletes faster, higher or stronger is uncertain.

"Just because you have more nitric oxide doesn't mean that you are going to be a better athlete," said Anthony Butch, director of the Olympic Analytical laboratory at UCLA. "If you have all the nitric oxide you need, and if you generate more from Viagra, it's not clear what effect that would have."

Some preliminary studies have shown that cyclists taking Viagra improved their performances by up to 40 percent.

ELSEWHERE

Blood tests at Trials: Swimmers and track-and-field athletes will be blood tested at this weekend's Olympic trials as part of the U.S. Anti-Doping Agency's ramped-up program to catch drug cheats. USADA unveiled its more aggressive approach — including more blood tests and targets on the so-called high-risk sports — last July.

Bulgaria weightlifters: Bulgaria's weightlifting federation will withdraw its team from the Beijing Games after 11 lifters tested positive for a steroid, the latest scandal to affect weightlifting ahead of the Summer Olympics. Eight members of the men's team and three women tested positive during out-of-competition tests conducted June 8-9, a federation statement said yesterday.

China's swimmer banned: China's top backstroker Ouyang Kunpeng has been banned for life for failing a doping test, just six weeks before the Beijing Olympics. In a statement yesterday, the Chinese Swimming Association said Ouyang tested positive for a doping substance on May 1. It gave no details about the substance. The CSA said Ouyang's coach Feng Shangbao was also given a life ban.